The present invention relates to a method of detecting and removing unstripped residual shell left on shellfish and to the apparatus for carrying out the method, and in particular, to a detection and removal method and an apparatus for carrying out the method, which are suited for use in inspecting whether there is residual shell on the flesh of shellfish such as shrimp or crab, after finishing shell-stripping work. It should be noted that by the expression xe2x80x9cshrimpxe2x80x9d in the present specification, all kinds of shrimp and shellfish which is similar to shrimp, such as lobster and prawn, etc. are included.
As the food service industry becomes increasingly popular, various kinds of food materials are now increasingly processed in great quantities and in a standardized manner in food processing factories. This trend is the same in the case of shellfish such as shrimp or crab. That is, large quantities of shellfish for which the shell-stripping work has been done are now brought into food processing factories as one raw material (food material) for various kinds of processed foods or retort pouch foods.
Usually, the work of stripping the shell left on shellfish is performed at a location near a fishing ground, and the shellfish whose shell has been stripped off is then immediately frozen and only the flesh portion of shellfish is brought into a food processing factory. The work of stripping the shell from shellfish is generally performed manually, since the separation of the shell from the flesh can be relatively easily performed. However, it is still difficult to perform the shell-stripping work faultlessly, thereby failing to eliminate the possibility that shellfish with residual shell remaining on the flesh, or with a portion of removed shell or leg inadvertently mixed with the flesh, may be brought into the food processing factory. Therefore, a package of flesh portion of shellfish that has been brought into the food processing factory after finishing the shell-stripping work is usually investigated after unpacking through visual observation to see if there is a piece of shell intermingled with the flesh or residual shell left unremoved from the flesh. If a piece of residual shell is found in the flesh portion of shellfish, the piece of residual shell is manually removed therefrom.
In the case of most of shellfish, the shell thereof is discolored as it is heat-treated. Due to this discoloration of the shell, it can be relatively easily distinguished from the flesh portion thereof. Before heat-treatment, however, both the flesh portion and the shell thereof are whitish in most shellfish. Additionally, the residual shell that might be left on the flesh portion of shellfish is generally small in size. Therefore, it is difficult, before heat-treatment of shellfish, to visually distinguish the residual shell from the flesh portion even if a piece of residual shell is left in the flesh portion thereof, thus leaving the residual shell overlooked or unidentified occasionally. If a piece of shell is left intermingled in processed foods or retort foods, it would compromise the taste of consumers, and diminishing the commercial value thereof.
The present invention has been made under such circumstances, and therefore, an object of the present invention is to provide a method of detecting and removing unstripped residual shell left on shellfish, which is suited for easily and reliably determining if there is any residual shell left on the stripped shellfish, thereby enabling the residual shell, if any, to be removed from the stripped shellfish. Another object of the present invention is to provide an apparatus for carrying out such a method.
With a view to solving the aforementioned problems, through extensive study and experiments conducted by the present inventors, it was finally found that when a light of a specific wave-range is irradiated onto shrimp or crab, a fluorescent light of a specific wave-range is emitted not from the flesh portion thereof but from the shell thereof. Namely, the present invention has been accomplished as a result of intensive study on this fact and is characterized by an irradiating light of a specific wave-range onto stripped shellfish after finishing the shell-stripping work thereof then, on the basis of information regarding the intensity of fluorescent light emitted from the shellfish, determining if there is any residual shell on the stripped shellfish, and subsequently removing any residual shell.
An alternative method of detecting and removing unstripped residual shell left on shellfish according to the present invention is characterized by irradiating a light of specific wave-range onto stripped shellfish after finishing the shell-stripping work thereof, taking an image of the stripped shellfish with a CCD camera, and on the basis of information on the intensity of fluorescent light emitted from the image of shellfish, determining if there is any residual shell on the stripped shellfish, and subsequently removing any residual shell.
By the expression of xe2x80x9ca light of specific wave-rangexe2x80x9d, it is meant a light of wave-range which is capable of causing emission of a fluorescent light more from the shell than from the flesh portion of a shellfish. For example, in the case where the shellfish is xe2x80x9cshrimpxe2x80x9d, the wave-range of the light is preferably is not more than 400 nm, more preferably around 250 nm. In the case where the shellfish is xe2x80x9ccrabxe2x80x9d, the wave-range of the light is preferably is not more than 400 nm.
The apparatus for detecting and removing unstripped residual shell left on shellfish according to the present invention for achieving the aforementioned object is suited for use in carrying out the aforementioned method, and comprises a means for irradiating a light of specific wave-range onto stripped shellfish after finishing the shell-stripping work thereof; a detection means for detecting fluorescent light emitted from said shellfish; means for determining if there is residual shell on the stripped shellfish on the basis of information obtained from said detection means; and means for removing residual shell, if any, on the basis of information from said determining means.
The means for irradiating a light is a means for irradiating an excitation light having the aforementioned wave-range. The detection means may be provided with a filter which is capable of absorbing light of a specific wave-range emitted from the aforementioned light-irradiating means, but capable of allowing at least the fluorescent light emitted from the shellfish to pass therethrough. The aforementioned determining means should preferably be designed such that when the intensity of fluorescent light obtained from said light detection means exceeds a given threshold value, it determines the existence of residual shell. The means for removing the residual shell is designed to be actuated on the basis of the determination that there is residual shell, and can be constituted for instance by a device which makes use of air blowing for removing the residual shell or shellfish having the residual shell.
An alternative apparatus for detecting and removing unstripped residual shell left on shellfish, which is suited for use in carrying out the aforementioned method, is characterized in that it comprises; a means for irradiating light of a specific wave-range onto stripped shellfish after finishing the shell-stripping work thereof; a CCD camera disposed to face said stripped shellfish; a means for determining if there is residual shell on the stripped shellfish on the basis of information on the intensity of fluorescent light that can be obtained from the image taken by said CCD camera; and means for removing residual shell, if any, on the basis of information from said determining means.
The means in this alternative apparatus for irradiating light may be the same as that of the first mentioned apparatus. The CCD camera may be selected from those which are conventionally known, and may be either a black-and-white CCD camera or a color CCD camera. Where the CCD camera is constituted by a black-and-white CCD camera, the aforementioned determining means should preferably be designed such that each of the image signals from the black-and-white CCD camera is preferably binarized, and that when the number of pixels to be derived from fluorescent light obtained from the shellfish precisely speaking emitted from the shell of shellfish exceeds a given threshold value, it determines the existence of residual shell. On the other hand, where the CCD camera is constituted by a color CCD camera, the aforementioned determining means should preferably be designed such that the color of the fluorescent light emitted from the shell is designated, by means of an image processor, and when the number of pixels in the designated area exceeds a given threshold value, it determines the existence of residual shell. The means for removing the residual shell may be the same as that of the first mentioned apparatus.